[BUG] Issue with dictionary definition and the openapi-generator

Description

I try to generate Java (Spring) code for the openapi 3.1.0 spec file listed below using the openapi gradle plugin version 6.2.1

The type Module should have a simple id and a map from String to String. Using additionalProperties is the way to define maps according to the official openapi specification https://spec.openapis.org/oas/v3.1.0#parameter-object-examples

However, it fails with the follwing Exception:

java.lang.IllegalArgumentException: Cannot deserialize value of type java.lang.Boolean from Object value (token JsonToken.START_OBJECT)
at [Source: UNKNOWN; byte offset: #UNKNOWN]

It seems, additionalProperties expects to be a boolean, and indeed, if I change the line to

additionalProperties: true

the code generation succeeds and generates a Map<String, Object>. However, I would like to specify the value type. In fact, I don't want simple string values but a more complex types using

additionalProperties:
  $ref: '#components/schemas/MetaDataItem'

which fails with the same exception.

openapi-generator version

6.2.1

OpenAPI declaration file content or url

openapi: 3.1.0
info:
  title: My-API
  version: 0.0.1
paths:
  /module:
    get:
      operationId: listModules
      summary: get modules
      tags:
        - Modules
      responses:
        "200":
          description: OK
          content:
           application/json:
            schema:
              $ref: '#/components/schemas/Module'

components:
  schemas:
    Module:
      type: object
      description: A module
      properties:
        id:
          type: string
          format: uuid
        metaData:
          type: object
          additionalProperties:
            type: string

Generation Details

Here is the gradle plugin task

task generateSpringServerClasses(type: org.openapitools.generator.gradle.plugin.tasks.GenerateTask) {
    generatorName = "spring"
    inputSpec.set(f.getCanonicalPath().toString()); // btw, another issue regarding windows paths 
    outputDir = "$buildDir/generated".toString()
    apiPackage = "myorg.api"
    invokerPackage = "myorg.invoker"
    modelPackage = "myorg.model"
    modelNameSuffix = "Dto"

    configOptions[

    ]
}

Steps to reproduce

• Have a gradle project with openapi generator plugin 6.2.1
• add the quoted spec file to project resources
• add the gradle task as quoted above
• run the gradle task

Related issues/PRs

There is also a Stackoverflow question https://stackoverflow.com/questions/74741536/issue-with-dictionary-definition-and-the-openapi-generator?noredirect=1#comment131912949_74741536

Suggest a fix

Start with the supplied OpenAPI 3.1.0 schema and the Gradle generateSpringServerClasses task using openapi-generator 6.2.1. Reproduce the failure with typed additionalProperties, then verify that generation succeeds and produces the intended Map<String, String> or referenced value type without the Boolean deserialization exception.